History of Developmental Biology + the Germ Layers

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Transcript of History of Developmental Biology + the Germ Layers

1600s1800s198519901925History of Developmental BiologyPre-scientific PeriodEarly Scientific PeriodIncreased interest in the anatomy of the fetus as well as other structuresBased knowledge on classical concepts by Aristotle and Galen, rather than obsevationScientific Revolution of the 17 CenturyBroke away from the classical observations (Harvey)Discovery of optical instruments = means to learn more. Recapitulation PeriodNew philosophy: romanticismFocus on studying nature and its changeabilityout with the old, in with the new ideasDevelopmental MechanicsScientists oppose Haeckel's recapitulation theory. e.g. His: embryogenesis is the product of mechanical forces. more experimentation led to more discoveriesBiochemistry and Cell biologyMore questions arise as to how differentiation and specification occurs. Organizer considered to be hormonal.New methods of examination e.g. electron microscopeFocus on cells rather than the embryoimportance of nucleus as the holder of genetic information; cloningnow called 'developmental biology'.Molecular Biology and Genetic Engineeringmolecular biology offered scientific techniques that were used in embryology.developmental biology and evolutionmedical applications in embryologyFuture: genetic engineering through further merging of biology and molecular techniques. Stem cell research

access to study embryos or gain knowledgeEgyptians and Babylonians were interested in congenital defects Hippocrates studied chicken embryosAristotleclassified animals according to whether they lay eggs, spontaneous generation, and viviparityGalenGreeks were highly interested in this matter Leonardo da Vinci VesaliusMalpighiDescartes' mechanical philosophyMicroscopists claim to see homunculi in eggs or spermSpeculations about the age of the EarthPreformation Theorymicroscopy of chick embryosclaimed to have seen a fully formed embryo in an unincubated eggEpigenesisthe structures of the adult formarise progressively during developmenteverything in the embryos is preformed

August WeismannMosaicism - aspects of the final pattern are already arranged in the embryo. If part of the embryo is destroyed a corresponding part of the adult is lost.Supported by Conklin’s study of ascidian embryos

Styela 1905

pigment in myoplasmcells to become tail musclehow cells become different1880sDetermination - a stable change in the internal state of a cellThe state of determination of cells can be tested by Transplantation.

Specification - cell will develop according to their fate even when isolated.

Discovery of the Organizer by Spemannpreformationgerminal selectionepigenetic reactions between cellsStem cells The Germ LayersGastrulation is the process through which cells sort out to generate the body planGastrulation involves the inward movement of cell from the epiblast

Early embryonic development

Topologies differ but a common theme -Ectoderm precursors are segregated from early from Progenitors that give rise to mesoderm and endoderm